1. Field of the Invention
The present invention generally relates to an organic electrically conductive compound, and an organic electroluminescent device including an organic luminous layer, or an organic luminous layer and one or more organic carrier transportation layers, sandwiched between a cathode and an anode.
2. Description of the Related Art
It is hoped that an organic electroluminescent device is utilized as a display device in various display apparatuses and a light source for illumination such as a backlight, etc., since bright emission can be obtained under application of a low voltage. FIG. 1 shows a typical structure of the organic electroluminescent device, which is a lamination structure of an transparent anode 2, an organic hole transportation layer 3 for efficiently transporting holes injected from the anode 2, an organic luminous layer 4 capable of emitting fluorescence, an organic electron transportation layer 5 for efficiently transporting electrons injected from a metal cathode 6, and the cathode 6, from bottom to top, on a substrate 1. The organic hole transportation layer 3, the organic luminous layer 4, and the organic electron transportation layer 5 are made from respectively suitable organic materials. When DC voltage is applied between both electrodes 2,6 of such an organic electroluminescent device, electrons are injected from the cathode 6 through the organic electron transportation layer 5 to the organic luminous layer 4 and occupy conduction levels of the layer 4, while holes are injected from the anode 2 through the organic hole transportation layer 3 to the organic luminous layer 4 and occupy valence levels of the layer 4. A fluorescent material constituting the organic luminous layer 4 is excited to a singlet excited state of the material by way of absorption of energy generated by recombination of the electrons moving on the conduction levels and the holes moving on the valence levels in the organic luminous layer 4. As the fluorescent material is energetically relaxed, the material emits fluorescence.
In the organic electroluminescent device with the typical structure as shown in FIG. 1, organic layers such as the organic hole transportation layer 3, the organic luminous layer 4, and the organic electron transportation layer 5 are commonly thin films made from insulating materials. Thus, in order to enable a sufficient electric current to flow through the organic layers under application of voltage to both electrodes 2,6, it has been needed to improve carrier (hole or electron) injection efficiency controlling an electrical conductivity on the interface between the electrode and the organic layer or between the organic layers, and carrier density and/or carrier mobility in the thin film of the organic layer. Specifically, a metal complex represented by tris(8-hydroxyquinolinato)aluminum (Alq), etc. and arylamines represented by bis[N-(3-methylphenyl)-N-phenyl]benzidine (TPD) and bis[N-(1-naphtyl)-N-phenyl]benzidine (xcex1-NPD) have been employed.
However, since the carrier injection efficiency on an interface between the electrode and the organic layer or between organic layers and the carrier density and carrier mobility in a thin film of the organic layer are low with respect to the organic electroluminescent device employing the above mentioned organic material, the electrical conductivity of the organic electroluminescent device is insufficient and it is required to apply high voltage between the electrodes. There is a problem in that application of the high voltage to both electrodes of the organic electroluminescent device could cause the service life of the device to be shortened.
Also, there is a further problem in that with respect to the organic electroluminescent device employing the above mentioned organic material, the temperature of the device becomes higher due to heat resulting from current carrying and fluorescence emission in the time of driving the device so that peeling on the interface between the cathode and the organic electron transportation layer and oxidation of the cathode could cause the device to deteriorate.
Accordingly, it is a general object of the present invention to provide an organic compound with a high electrical conductivity and a high heat resistance, in which the above problems are eliminated.
Another object of the present invention is to provide an organic electroluminescent device in which an organic luminous layer or at least one of an organic luminous layer and one or more organic carrier transportation layers contains the organic compound with a high electrical conductivity and a high heat resistance.
To achieve one of the above objects, the present invention provides an electrically conductive compound represented by general formula (1): 
wherein
n is an integer from 2 to 10,
k represents any of integers from 1 to n,
Ar1, Ar1xe2x80x2, Ar2, and Ar2xe2x80x2 are substituted or non-substituted aromatic hydrocarbon rings or heterocyclic rings that share a bond between carbons at 2,3-positions or 4,5-positions of a pyrrole ring in general formula (1) and are fused with the pyrrole ring, respectively, and
Rk and Rkxe2x80x2 are aliphatic hydrocarbon groups or substituted or non-substituted aryl or heterocyclic groups, respectively.
According to the present invention described above, an organic compound with a high electrical conductivity and a high heat resistance can be provided.
The present invention provides the electrically conductive compound described above, wherein at least one of Ar1, Ar1xe2x80x2, Ar2, and Ar2xe2x80x2 is different from the others and/or at least one of Rk and Rkxe2x80x2 (k=1, . . . , n) is different from the others. That is, all of Ar1, Ar1xe2x80x2, Ar2, and Ar2xe2x80x2 are not identical and/or all of Rk and Rkxe2x80x2 (k=1, . . . , n) are not identical.
According to the present invention described above, an organic compound with a high electrical conductivity, a high heat resistance and a high transparency can be provided.
The present invention provides an electrically conductive compound represented by formula (2): 
According to the present invention described above, an organic compound with an excellent electrical conductivity and an excellent heat resistance being easy to synthesize can be provided.
To achieve one of the above objects, the present invention provides an organic electroluminescent device including an organic luminous layer, or an organic luminous layer and one or more organic carrier transportation layers, sandwiched between a cathode and an anode, wherein the organic luminous layer or at least one of the organic luminous layer and the one or more organic carrier transportation layers contains any one of the electrically conductive compounds described above.
According to the present invention described above, an organic electroluminescent device can be provided in which an organic luminous layer or at least one of an organic luminous layer and one or more organic carrier transportation layers contains the electrically conductive compound with a high electrical conductivity and a high heat resistance.